The present invention relates to a novel and simple process for the simultaneous regeneration of spent bleaching earth and conversion of adsorbed oil to alkyl esters of C1 to C8 carbon atoms by using alcohols. The present invention particularly relates to an improved process for the recovery of oil and its insitu conversion to methyl esters. The regenerated spent bleaching earth is further activated at 120-500xc2x0 C. for 2-6 hours in a muffel furnace. The regenerated and activated earth can be reused for the bleaching of vegetable oils. The alkyl esters obtained after distillation find use as oleochemical feedstock.
The refining of oils requires several steps to remove components that are harmful to health, or that are deleterious to storage quality. The classical steps for this purpose are de-gumming, neutralizing, bleaching and deodorizing. Bleaching with active clay is an essential step in refining of vegetable oils. The bleaching process removes undesirable substances such as soap residues, traces of heavy metals, pesticide residues and residues of phosphorus compounds etc. apart from its main purpose of removal of coloring matter like carotenoids and chlorophyll pigments. Bleaching process is carried out by using heat, hydrogen, chemical additives or by adsorption on solids. Adsorptive bleaching not only removes the coloring matter but also fulfils the other requirements of the bleaching process. Bleaching clays employed for this process are alumino silicates containing magnesium, calcium and iron in varying proportions. These clays are subjected to acid treatment, which replaces the cations by protons, thereby increasing the internal surface area and the adsorptive capacity. Bleaching of vegetable oils is carried out at a dosage of 1-3% and the current worldwide production of greater than 60 million tons of oils is accompanied by production of spent clay containing 20-40% oil estimated at 600,000 tones. The disposal of spent bleaching clay from the vegetable oil processing industry is a problem of growing importance. Disposal of the spent earth by incineration, inclusion in animal feeds, land filling methods, or concrete etc. is generally practiced. It was a general practice to recover the fatty matter from the earth and discard the deactivated earth. The constant change in environmental legislation and the growing importance of safety in the disposal techniques has led to many restrictions in solid waste management. The earlier research on spent clay reclamation focused on the oil left in the spent clay and the clay itself was not regenerated for reuse. The recovered oil was used for industrial purposes. Recent studies are focusing not only on recovery of left over oil in the spent clay but also on regeneration of spent bleaching earth for reuse. The recovery of oil and reuse of spent bleaching earth are the areas where great opportunity exists for cost saving in the oil processing industry.
There are many patented methods and published literature available on regeneration of spent earth. Different methods proposed for the recovery of oil from spent earth have been reviewed by Kaufmann and Mukharjee (Fette, Seifen, Anstrichm. 1967, 69, 463) and recovery by water separation and solvent extraction were the most commonly reported methods. Thermal regeneration of spent alumina used for bleaching of cottonseed oil was done at 400-700xc2x0 C. followed by re-moisturizing the earth to ≈10%. Spent earth from the bleaching of edible oils is revived by washing with an organic solvent preferably acetone or methyl ethyl ketone. Kalam and Joshi (Journal of Am. oil Chem. Society, 1988, 65, 1917-1921) studied regeneration of deoiled spent earth in aqueous medium at a relatively lower temperature (170-270xc2x0 C.) in an autoclave. They achieved about 81% regeneration (reduction in red color only). Thus, the mechanism of regeneration was explained as, desorption of adsorbate from the surface of the adsorbent, intra-particle diffusion within pores to the outer surface of the adsorbent, mass transfer from adsorbent to the liquid bulk and finally possible degradation of adsorbate in liquid bulk. Kalam and Joshi (Journal of Am. oil Chem. Society, 1988, 65, 1536-1540) also reported regeneration of de-oiled spent earth by wet oxidation method using molecular oxygen at elevated temperatures of 125-350xc2x0 C. and pressure of 1-20 Mpa. in an autoclave. Thus chemical regeneration method was claimed to be clean, compact and cost effective. It proceeds via fragmentation of larger molecules into smaller molecules and finally oxidation to carbondioxide and water. Waldmann and Eggers studied de-oiling of bleaching clay by high-pressure extraction with carbondioxide as a solvent (Journal of Am. oil Chem. Society, 1991, 68, 922-930). The authors in their investigations compared the extractability of two different types of bleaching clays with carbondioxide as a solvent aiming a complete separation of the oil from the adsorbent and reuse of the later. Their results showed that oil of good quality could be recovered and the bleaching clay still has an activity of approximately 50% of fresh clay. The degree of extraction of oil for different experiments was in the range of 93 to 97%. There are many patents for the regeneration of spent bleaching earth which include an oxidation step in their process (GB Z189, 233, EP 05,29555, U.S. Pat. Nos. 5,256,613, 5,358,915, 5,468,701). Nebergall (INFORM, 1996, 7, 206-211) in his article on xe2x80x9cSpent bleaching earth regenerationxe2x80x94commercial scale resultsxe2x80x9d reviewed various pretreatment, extraction and post-treatment methods. He concluded that the autoclave extracted de-oiled clay produced regenerated clay far superior to that of the fresh clay. Thus all further work was done on various systems of oxidation and reactivation following an initial autoclave extraction on pilot-plant level for commercial viability. In this process due to the high temperature of processing in the autoclave, most of the adsorbed vegetable oil was converted to glycerol and free fatty acids. This step of the process recovered ≈65-70% of the organics present in the spent bleaching earth. The organics remaining on the bleaching earth i.e. chlorophyll pigments and carotenoids are burned onto the active sites by the oxidizing agent whereby they are reduced to a type of activated carbon resulting in superior performance of pilot plant regenerated clay than fresh clay. Surfacexe2x80x94and porexe2x80x94structures of de-oiled acidxe2x80x94and heat treated spent bleaching clays were studied after de-oiling by extraction with organic solvents (J. Am. Oil Chem. Soc., 1997, 74, 963-970). Acid and then heat treatment regenerated the de-oiled clays. Acidified heat-treated de-oiled samples had larger surface areas and greater pore volumes than fresh clay samples. Thus acid and heat treatments removed substances adsorbed in the pores that were not removed by solvents or carbondioxide extraction. A slight modification to the above process was the regeneration of spent bleaching earth first by thermal processing followed by acid treatment which resulted in the regenerated adsorbent with better properties (J. Chem. Technol. Biotechnol, 2000, 75, 773-776).
U.S. Pat. Nos. 4,469,805 and 3,472,786 disclose a process for removal of organic, polar type and nitrogen containing impurities from spent clay by percolating liquid methanol through a bed of spent clay. But in both cases, the spent clay was used to purify petroleum and not edible oil. In both cases, the oil present in the mixture was not converted into corresponding ester. However, the essential and non-obvious aspect of the present invention is the use of alcohol and the simultaneous conversion of the acids into its corresponding esters within a temperature range of 110xc2x0 to 270xc2x0 C. The treatment of spent clay in organic phase at high temperatures and moderate pressure results in simultaneous regeneration of clay and conversion of oils into ester. The high temperatures and efficient stirring increases the solubility of adsorbed species into the organic solvent phase resulting in desorption of adsorbates from the surface of the adsorbent. It also results in diffusion of species form within the adsorbent pores.
Thus, all the above methods involve pretreatment, regeneration, post-treatment and activation of the clay. Thus, development of a commercially viable simple process for the recovery of oil and regeneration of spent clay would be economically advantageous and also eco-friendly.
The main object of the present invention is to provide a novel process for the regeneration of the spent clay and conversion of oil recovered form the spent clay to alkyl esters.
Another object of the present invention is to provide a novel, simple and improved process for the regeneration of spent bleaching earth for reuse in bleaching of vegetable oils.
Yet another object of the present invention is to convert the recovered oil insitu to alkyl esters.
Still another object of the present invention is to use the alkyl esters thus obtained after distillation as the oleochemical feedstock.
The present invention relates to a process for the simultaneous regeneration of spent bleaching earth and conversion of adsorbed oil to alkyl esters of C1 to C8 carbon atoms by using alcohols. The treatment of spent bleaching earth in organic phase at high temperatures and moderate temperature regenerates the spent clay.
Accordingly, the present invention relates to a novel process for simultaneous regeneration of spent clay used in refining vegetable oils and conversion of the vegetable oil recovered from the spent clay to alkyl esters of C1 to C8 carbon atoms, said process comprising: treating the spent clay with alcohols at a temperature in the range of 110xc2x0-270xc2x0 C. for 1-11 hours.
In a preferred embodiment of the present invention, the reaction is carried out at a pressure of 10 to 50 kg/cm2.
In another preferred embodiment of the present invention, the reaction is carried out at 130xc2x0 to 250xc2x0 C. for 4 to 11 hours at a pressure of 15 to 40 Kg/cm2.
In yet another preferred embodiment of the present invention, the reaction is carried out at 170xc2x0 to 230xc2x0 C. for 2 to 8 hours at a pressure of 15 to 30 Kg/cm2. In an embodiment of the present invention, the spent clay is a by-product obtained during bleaching of oil.
In another embodiment of the present invention, the spent clay contains 20-40% of oil.
In yet another embodiment of the present invention, the ratio of clay to alcohol varies from 1:0.5 to 1:2.5.
In still another embodiment of the present invention, the alcohols are selected from straight-chained or branch-chained alcohols.
In one more embodiment of the present invention, the alcohol is selected from C1 to C8 alcohols.
In one more preferred embodiment of the present invention, the alcohol is methanol and the ester obtained is methyl ester.
In one another embodiment of the present invention, the alcohol is present in excess by 10 to 30 moles.
In one another preferred embodiment of the present invention, the alcohol is present in excess by 20 moles.
In an embodiment of the present invention, the process comprises of insitu recovery and conversion of the oil to methyl esters.
In yet another embodiment of the present invention, the spent clay required minimum steps for regeneration.
In still another embodiment of the present invention, the regeneration of spent earth does not require any pretreatment or any conventionally used oxidizing agent. In one more embodiment of the present invention, the process involves thermal activation of the clay for reuse as bleaching earth.
In one another embodiment of the present invention, the regenerated spent clay is activated by heating it at 120xc2x0 to 500xc2x0 C. for 2 to 6 hours.
In one another preferred embodiment of the present invention, the above-reactivated earth is capable of bleaching the vegetable oils.
In another embodiment of the present invention, the bleaching of vegetable oils using above regenerated earth does not require any additional carbon.
In still another embodiment of the present invention, the yield of ester ranges from 40 to 70 per cent.
In yet another embodiment of the present invention, the process is economically advantageous, commercially viable and eco-friendly. The broad applicability of the invention was examined by reacting the spent bleaching earth with different alcohols to get different esters and regeneration of spent clay by heat treatment after removal of alcohol soluble material.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.